1. Field of the Invention
This invention relates to a probe head for testing the electrical properties of a semiconducting device under test. More particularly, the probe head contacts both sides of the semiconducting device under test and can receive electrical and optical inputs. The probe head is particularly effective for testing the characteristics of a light emitting diode (LED).
2. Description of the Related Art
An LED is a semiconductor device that emits incoherent monochromatic light when electrically biased in a forward direction. The effect is a form of electroluminescence with the color and wavelength dependent on the semiconducting material used. For example, aluminum gallium arsenide generates red and infrared light, gallium nitride generates green light, and zinc selenide generates blue light.
FIG. 1 illustrates an LED 10 (also referred to as semiconducting device 10 or device 10) as known from the prior art. The LED 10 includes first 12 and second 14 electrically conductive contact pads located on opposing first 16 and second 18 sides of the LED. When a direct current voltage is impressed across the first 12 and second 14 contact pads and biased in the proper direction, the LED 10 emits light 20.
With reference to FIG. 2, the electrically conductive contact pads and other features of the LED 10 are typically formed by doping a wafer 22. It is necessary to test the electrical and optical characteristics of the LED. Such testing is conventionally done at the wafer 22 stage prior to singulation of the LEDs 10.
Interference from adjoining LEDs may influence the electrical and optical data acquired during wafer stage test. More accurate measurement of LED characteristics may be obtained if testing is performed following singulation.